1. Field of the Invention
The present invention relates to a lens barrel adapted for enabling a two-group type zoom lens system to be used as a so-called "one-hand zoom lens system" which is capable of achieving both zooming and focusing actions by a single operating sleeve.
2. Background of the Invention
While several types of zoom lens system are known, the two-group type features a compact overall size and achieves zooming by operation of mobile front and rear lens units and effects focusing by displacement of the front unit alone. FIG. 6 shows an illustrative design of the profile of displacements of the front lens group, F, and of the rear group, R, which occur when the focal length of a two-group type zoom lens system is varied from 36 mm to 68 mm. As is apparent, the amount of displacement of the front lens group F on the narrow-angle side is considerably larger than that of the rear group R.
A two-group zoom lens system having this characteristic in association with lens displacement is not adapted to one-hand operation in which the rear lens group is moved by displacing the front group (operating sleeve) in the direction of the optical axis. In order to solve this problem, Japanese Utility Model Publication No. 51786/1977 proposes the use of two separate operating sleeves, one for zooming and the other for focusing purposes. In other conventional zoom lens system, the direction of displacement of the front lens group F coincides with that of the rear group R on the narrow-angle side as indicated by the dashed line in FIG. 6. In this case, it is absolutely impossible to fabricate a one-hand type zoom lens barrel by employing the conventional system.
On the other hand, a one-hand zoom lens barrel has been realized for 4-group zoom lens systems as shown in Japanese Patent Publication No. 80010/1981. However, with the zoom lens system of the four-group type, only the two intermediate groups, namely, the variator group and compensator group, are displaced during zooming, and none of the problems associated with the two-group type system described above will occur.